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<body>
<h1 id="v-bind-class-style-">v-bind及class与style绑定</h1>
<p><code>v-bind</code>的主要用法是动态更新HTML元素上的属性。</p>
<p>在数据绑定中，<code>v-bind</code>最常见的两个应用就是元素的样式名称<code>class</code>和内联样式<code>style</code>的动态绑定。</p>
<h2 id="-class-">绑定<code>class</code>的几种方式</h2>
<h3 id="-">对象语法</h3>
<p>给<code>v-bind:class</code>设置一个对象，可以动态地切换<code>class</code>：</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;div :class=&quot;{&#39;active&#39;:&#39;isActive&#39;}&quot;&gt;测试文字&lt;/div&gt;
&lt;/div&gt;

new Vue({
    el: &quot;#app&quot;,
    data: {
        isActive: true
    },
});
</code></pre><p>对象中也可以传入多个属性，动态切换<code>class</code>。另外，<code>:class</code>可以与普通<code>class</code>共存。</p>
<pre><code>&lt;div class=&quot;static&quot; :class=&quot;{&#39;active&#39;:&#39;isActive&#39;,&#39;error&#39;:isError}&quot;&gt;测试文字&lt;/div&gt;

data: {
    isActive: true,
    isError: false
}
</code></pre><p>当<code>:class</code>的表达式过长或逻辑复杂时，还可以绑定一个计算属性。当条件多于两个时，都可以使用<code>data</code>或<code>computed</code>。</p>
<p>除了计算属性，也可以直接绑定一个Object类型的数据，或者使用类似计算属性的<code>methods</code>。</p>
<h3 id="-">数组语法</h3>
<p>当需要应用多个<code>class</code>时，可以使用数组语法，给<code>:class</code>绑定一个数组，应用一个<code>class</code>列表：</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;div :class=&quot;[activeCls,errorCls]&quot;&gt;测试文字&lt;/div&gt;
&lt;/div&gt;

new Vue({
    el: &quot;#app&quot;,
    data: {
        activeCls: &#39;active&#39;,
        errorCls: &#39;error&#39;
    }
});

// 结果
&lt;div class=&quot;active error&quot;&gt;测试文字&lt;/div&gt;
</code></pre><p>也可以使用三元表达式来根据条件切换<code>class</code>：</p>
<pre><code>&lt;div :class=&quot;[isActive ? activeCls : &#39;&#39;,errorCls]&quot;&gt;测试文字&lt;/div&gt;

new Vue({
    el: &quot;#app&quot;,
    data: {
        isActive: true,
        activeCls: &#39;active&#39;,
        errorCls: &#39;error&#39;
    }
});
</code></pre><p>当<code>class</code>有多个条件时，可以在数组语法中使用对象语法：</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;div :class=&quot;[{&#39;active&#39;:isActive},errorCls]&quot;&gt;测试文字&lt;/div&gt;
&lt;/div&gt;
</code></pre><p>使用计算属性给元素动态设置类名，在业务中经常用到，尤其是在写复用的组件时，所以在开发过程中，<strong>如果表达式较长或逻辑复杂，应该尽可能地优先使用计算属性</strong>。</p>
<h3 id="-">在组件中使用</h3>
<p>如果直接在自定义组件上使用<code>class</code>或<code>:class</code>，样式规则会直接应用到这个组件的根元素上。</p>
<pre><code>Vue.component(&#39;my-component&#39;, {
    template: `&lt;p class=&quot;article&quot;&gt;一些文本&lt;/p&gt;`
});
</code></pre><p>然后在调用这个组件时，应用对象语法或数组语法给组件绑定<code>class</code>：</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;my-component :class=&quot;{&#39;active&#39;:isActive}&quot;&gt;&lt;/my-component&gt;
&lt;/div&gt;
</code></pre><p>这种用法仅适用于自定义组件的最外层是一个根元素，否则会无效。当不满足这种条件或需要给具体的子元素设置类名时，应当使用组件的<code>props</code>来传递。</p>
<h2 id="-">绑定内联样式</h2>
<p>使用<code>:style</code>可以给元素绑定内联样式，方法与<code>:class</code>类似，也有对象语法和数组语法，很像直接在元素上写CSS。</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;div :style=&quot;{&#39;color&#39;:color, &#39;fontSize&#39;:fontSize+&#39;px&#39;}&quot;&gt;文本&lt;/div&gt;
&lt;/div&gt;

new Vue({
    el: &quot;#app&quot;,
    data: {
        color: &#39;red&#39;,
        fontSize: 14
    }
});
</code></pre><p>一般把样式写在<code>data</code>或<code>computed</code>中：</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;div :style=&quot;styles&quot;&gt;文本&lt;/div&gt;
&lt;/div&gt;

new Vue({
    el: &quot;#app&quot;,
    data: {
        styles: {
            color: &#39;red&#39;,
            fontSize: 16 + &#39;px&#39;
        }
    }
});
</code></pre><p>在实际业务中，<code>:style</code>的数组语法并不常用，可以写在一个对象里面，而较为常用的是计算属性。</p>
<p>另外，使用<code>:style</code>时，Vue.js会自动给特殊的CSS属性名称增加前缀，比如<code>transform</code>。</p>

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